In Tableau Online, when refreshing a workbook with embedded data sources, or when refreshing a published data source, the refresh may fail with the following error:
Error: com.tableausoftware.nativeapi.dll.DataSourceException: [Microsoft][SQL Server Native Client 11.0]Named Pipes Provider: Could not open a connection to SQL Server  [Microsoft][SQL Server Native Client 11.0]Login timeout expired [Microsoft][SQL Server Native Client 11.0]A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online. Unable to connect to the server "<SERVER NAME>". Check that the server is running and that you have access privileges to the requested database.